Dredging Up the Past

David Hilton, a geochemist at the Scripps Institution of Oceanography at University of California San Diego led a team to the western Pacific Ocean to examine the rocks from deep-sea volcanoes to learn about the slow but steady tectonic movements of the earth.

The Lau Basin, located between the islands of Fiji and Tonga in the Western Pacific, is of great curiosity to geologists since it comprises a subduction zone, a region where two tectonic plates collide leading to the formation of an arc of active deep-sea volcanoes, and a basin where crust is being stretched thin across the seafloor. Volcanoes are located in areas where the movement of tectonic plates causes cracks in the earth's crust and molten lava from the earth's mantle erupts to the surface. These molten lava rocks hold unique clues about Earth's inner workings and the source of explosive volcanic eruptions.

We assembled a scientific party of eight - six from Scripps Oceanography and two from San Diego State University - and in October 2006 flew to Fiji where we made last-minute plans for the cruise as well as took in a few sites. In no time at all, we set off aboard R/V Melville for the international dateline, where the Lau Basin is located, and started dredging.

Our aim was to survey the northern part of the basin and collect rocks from a number of seamounts in the area. Did I forget to mention that the Lau Basin is underwater? Well, it is. The seamounts - underwater volcanoes - can be found at a depth between two and three kilometers, so the only way to get the rocks is by dredging.

We dredged around the clock for the six days we were at the site, retrieving over 2 tons of precious rocks from the seafloor. We still managed to have time for seminars from the world's leading scientific expert on the region - Dr. James Hawkins, Scripps professor emeritus. Hawkins led many groundbreaking research expeditions to the Lau basin in the past. He recently retired from his active teaching duties so his vast knowledge aboard was invaluable and the intimate lectures were a treat for the research team. Our opportunity to work in the Lau Basin was made possible by support from UC Ship Funds, which offers support to Scripps scientists to teach and conduct research aboard the Scripps research fleet.

We completed our R/V Melville cruise in Samoa and used the opportunity for some more rock collecting - this time on land - it's much easier! We also visited Vailima - not only the name of the local brew but, more importantly, the home of Robert Louis Stevenson - of Treasure Island fame.

— David Hilton, professor of geochemistry at Scripps Institution of Oceanography, University of California San Diego